BMI Calculator
Calculate your Body Mass Index from height and weight in metric or imperial units and see the matching WHO weight category instantly.
BMI Calculator — A fast BMI (Body Mass Index) calculator that turns your height and weight into a single number and the matching World Health Organization weight category. Switch between metric (cm, kg) and imperial (in, lb) units, type your two figures, and the result updates as you type. Every calculation runs entirely in your browser, so the numbers you enter never leave your device.
What is BMI Calculator?
The BMI Calculator estimates Body Mass Index, a widely used screening figure that relates a person's weight to their height. It is used by individuals tracking fitness goals, by clinicians for a quick first look, and by anyone curious where they sit relative to standard ranges. Choose your unit system with the segmented control in settings, enter your height and weight, and the read-only result field shows your BMI rounded to one decimal place. Below it, a category label maps your number onto the WHO ranges: underweight, normal, overweight, or obese. BMI is a general screening number, not a diagnosis, and it does not account for muscle mass, body composition, age, or sex.
How to use BMI Calculator
- Open settings and pick your unit system: metric (cm and kg) or imperial (in and lb).
- Type your height into the height field, in the unit shown on its label.
- Type your weight into the weight field, in the unit shown on its label.
- Read your BMI in the read-only result field; it recalculates automatically as you type.
- Check the category label below to see which WHO range your BMI falls into.
Examples
Metric: 170 cm, 65 kg
Input
System: metric, height = 170 cm, weight = 65 kg
Output
BMI 22.5 — Normal
Metric: 160 cm, 80 kg
Input
System: metric, height = 160 cm, weight = 80 kg
Output
BMI 31.3 — Obese
Imperial: 70 in, 150 lb
Input
System: imperial, height = 70 in, weight = 150 lb
Output
BMI 21.5 — Normal
Frequently asked questions
- How is BMI calculated?
- BMI is weight in kilograms divided by the square of height in meters (kg / m²). Imperial inputs are converted first: inches are multiplied by 0.0254 to get meters and pounds by 0.453592 to get kilograms, then the same formula is applied.
- What do the categories mean?
- This tool uses the standard WHO ranges: below 18.5 is underweight, 18.5 to 24.9 is normal, 25 to 29.9 is overweight, and 30 or above is obese.
- Is BMI an accurate measure of health?
- BMI is a quick screening number, not a diagnosis. It does not distinguish muscle from fat and does not account for body composition, age, or sex, so a very muscular person can read as overweight. Treat it as one general indicator, not a complete picture.
- What happens if I leave a field blank or enter zero?
- If a field is empty, not a number, or zero or negative, the result and category show a dash (—). Height must be greater than zero because BMI divides by height squared.
- Are my numbers sent to a server?
- No. Every calculation runs 100% client-side in your browser with no upload and no server communication, so the height and weight you enter never leave your device.
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